Material guide: isobutyl quinoline — one molecular formula, five records, and a tenfold spread in recommended evaluation strength

Short version: this series has a rule — check the CAS, not the name. This material is that rule's cleanest example: five records, one molecular formula, five CAS numbers, and a tenfold spread in recommended evaluation strength. Buying the wrong isomer does not break anything; it just makes something else.

The five records

Database name	CAS	Suppliers	Strength	Recommended eval	Substantivity	Odour
6-isobutyl quinoline	68141-26-4	0	—	—	—	(no field)
6(or 8)-isobutyl quinoline	68198-80-1	3	Medium	1%	> 48 h	Earthy, rooty, nutty, oakmoss, vetiver, leathery, green
2-isobutyl quinoline	93-19-6	5	High	10%	160 h	Animal, leathery, woody, rooty, oakmoss, tobacco
isobutyl quinoline (Pyralone, Givaudan)	65442-31-1	22	High	10%	168 h	Castoreum, leathery, earthy, oakmoss, vetiver
isobutyl quinoline (4-isobutyl)	1333-58-0	7	High	1%	168 h	Leathery, animal, herbal, green

Every one is C13H15N with MW 185.27. They are isomers of the same molecule, differing in where the isobutyl group sits on the quinoline ring.

And the differences below are not rounding:

• Recommended evaluation strength differs tenfold. 93-19-6 and 65442-31-1 say 10%; 1333-58-0 and 68198-80-1 say 1%. Dilute by the wrong row and you are an order of magnitude out.
• Supplier counts run from 0 to 22. 68141-26-4 has no supplier record at all; you cannot buy it. The easiest to obtain is Pyralone (65442-31-1, 22 suppliers).
• The odour fields have different centres of gravity. 93-19-6 reads "animal, leathery, tobacco"; 65442-31-1 reads "castoreum, leathery"; 1333-58-0 reads "leathery, animal, herbal, green"; and 68198-80-1 reads "earthy, rooty, nutty" with leather sixth.

The suppliers themselves separate them

The most persuasive evidence sits in the database's solubility field, which is where supplier odour notes get crammed. Givaudan describes two of them separately:

Butyl Quinoline Secondary (68198-80-1): "Odor: Leather, Green, Woody, Earthy, Powerful. Use: Butyl Quinoline Secondary has a smooth, fine, woody-vetiver-leather character. It is used in chypre, leather, woody compositions and in masculine colognes where it imparts great diffusion and fixation."

Pyralone (65442-31-1): "Pyralone is finer, more aromatic and tobacco-like, and has less of a dry, earthy character than Butyl Quinoline Secondary. It is used in chypre, fougère and tobacco accords."

Isobutyl Quinoline-2 (93-19-6): "Odor: Leather, Woody, Powerful. Use: Isobutyl Quinoline is used in chypre, leather and woody compositions. It is widely used in masculine colognes where its vibrant, intense leather character can be used to great advantage. Isobutyl Quinoline is extremely powerful and long lasting."

"Pyralone has less of a dry, earthy character than Butyl Quinoline Secondary" is written by the manufacturer, and it happens to be exactly the axis the poster in this round's beginner article cared about.

The person after a clean, light, white suede wrote "Pyralone / IBQ (1% in DPG)" in his formula, two names on either side of a slash. They are not the same thing. If he wants to avoid the dark, earthy side, that one line bears directly on the goal.

Doses in the corpus

Across 954 published formulas, quinolines under all spellings appear in 28 (2.9%), at a median share of 1.12%.

Spelling	Formulas
isobutyl quinoline	15
para-methyl tetrahydroquinoline	4
isopropyl quinoline	3
2-isobutyl quinoline	2
para-methyl quinoline	2
6-sec-butylquinoline	1
iso butyl quinoline (iff)	1

Seven spellings. And the most common of them, plain "isobutyl quinoline" at 15 formulas, maps to two different CAS numbers in the database — 65442-31-1 and 1333-58-0 — whose recommended evaluation strengths are 10% and 1% respectively.

When a formula says "isobutyl quinoline", you do not know which one the author used. That is not carelessness on the author's part; the name itself is insufficient.

The median dose of 1.12% also needs reading carefully. For a material at strength rank 3 with evaluation recommended at 10% or less, 1% in a formula is a substantial amount. I have not listed an interquartile range for those 28, because the sample is spread across seven spellings that may be different molecules, and pooling their doses is questionable to begin with. The median is here for scale, not as a dosing recommendation.

What this material does

Taking Pyralone (65442-31-1, 22 suppliers) as the representative:

Field	Value
Appearance	Yellow to dark brown clear liquid (est)
Assay	95–100% (sum of isomers)
Boiling point	288.3 °C @ 760 mmHg
Specific gravity	1.007–1.015 @ 25 °C
Refractive index	1.577–1.583
logP	3.90 (est)
Water solubility	101 mg/L @ 20 °C (exp)
Strength	High; evaluation recommended at 10% or less (rank 3)
Substantivity	168 hours at 100%
Natural occurrence	Not found in nature
Shelf life	24 months
Oral toxicity	Rat LD50 1020 mg/kg

Note that the assay field says "sum of isomers 95–100%". Pyralone is itself an isomer mixture, not a single molecule, which is why its CAS (65442-31-1) differs from the pure 2- and 4-isomers.

Substantivity of 168 hours — seven days — with strength rank 3 and no natural occurrence. This is a classic high-strength fixative material: whatever you put in stays a long time, so the cost of a mistake runs a week.

Its listed applications include chypre, fougère, tobacco accords, amber and animal directions, plus a few classic perfume names (Bandit, Cabochard, Cachet). Those are twentieth-century leather chypres — this is the molecule of that era's leather.

Practical advice for a beginner

• Ask the supplier for the CAS before buying. The name "isobutyl quinoline" maps to five records here, one of which has no supplier at all.
• The most widely stocked is Pyralone (65442-31-1, 22 suppliers), so if you just want one that works, that is the easiest to obtain.
• To avoid the earthy, rooty side, avoid 68198-80-1 (Butyl Quinoline Secondary) — the manufacturer itself says Pyralone has less of that dry earthy character.
• Dilute according to the recommendation for the one you actually bought. 10% and 1% differ tenfold, and both appear among these five.
• Start at the 0.01% level. Strength rank 3 and 168 hours of substantivity together mean the cost of getting it wrong is high.

On individual differences

This round's beginner article covered an exchange from the same thread: someone says cashmeran smells like wet mud to them, and another replies that cashmeran smells differently to him, which is why this hobby is so difficult.

That matters particularly for the quinolines, because their odour fields already disagree — the same molecular family, recorded by some as "leather, tobacco" and by others as "earthy, rooty, nutty". Some part of that disagreement may not be a difference in molecules but a difference in noses.

Knaapila's 2012 twin study measured a panel of chemosensory stimuli including a perfumery musk, Galaxolide™, and found that individual differences were stable over time for most traits, with heritability h² from 0.41 to 0.71 for some, confirming prior genotype-phenotype associations for androstenone among others. A 2022 dataset from central Russia (807 participants) notes that androstenone is perceived as unpleasant by roughly a quarter of the population.

Neither study measured any quinoline. I cite them for one thing only: when two records give different odour fields for the same material, "one of them is wrong" is not the only explanation.

What this doesn't establish

• I have not compared the actual smell of these five. The whole piece rests on database fields and supplier notes.
• The 1.12% median across 28 corpus formulas pools seven spellings that may correspond to different molecules. It is good for scale only.
• The database gives no breakdown of the "sum of isomers" in 65442-31-1. What proportion each isomer holds in Pyralone, I do not know.
• 68141-26-4 has zero suppliers and almost empty fields. It is listed to show how many records sit under this name, not because I know anything about it.
• I could not find the basis for the 1% versus 10% difference in recommended evaluation strength. This series has already measured that only 1.9% of database materials carry that field, and that the database does not document how it is set.
• Neither cited paper measured quinolines or Cashmeran. What they establish is the general point that individual differences are real and partly heritable.